A splice variant of a gene results from a selective transcription of the exons of the gene. Each multi-exon gene has a transcription start site (i.e., TATA box), promoter elements, exons and introns, and a transcription end site (i.e., a poly-adenylation site). The splicing machinery removes introns and splices adjacent exons together to form mRNA. The promoter elements regulate the removal of introns and splicing of adjacent exons in a way that is tissue specific. The mRNA may then be translated into active or inactive proteins. FIG. 1 is a block diagram illustrating the transcription of a gene into mRNA. In this example, gene 101 includes exons 1-5 and introns 1-4. (The pre-mRNA phase of transcription is not depicted in FIG. 1.) The mRNA 102 illustrates a splice variant that is specific to brain tissue. The mRNA 102 includes exons 1-5. The transcription start site is the TATA box, and transcription end site is the poly-A tail. The mRNA 102 includes four exon-exon junctions, that is the junctions between exon 1 and exon 2, exon 2 and exon 3, exon 3 and exon 4, and exon 4 and exon 5. The mRNA 103 illustrates a splice variant that is specific to heart tissue. The mRNA 103 includes exon 1, exon 2, exon 4, and exon 5. Exon 3 was omitted during the transcription process; it is thus an optional exon in the splice variants. The mRNA 103 includes three exon-exon junctions that is, the junctions between exon 1 and exon 2, exon 2 and exon 4, and exon 4 and exon 5.
It is generally considered that the complexity of higher organisms is achieved by the diversity of expressed proteins, which are regulated by the alternate splicing of genes. Alternate splicing increases the protein diversity by allowing multiple, sometimes functionally distinct, proteins to be encoded in the same gene. The variants of a given gene can be specific to tissue and to developmental and pathological states. Splice variants that result in inactive proteins and pathological conditions may provide useful links between genotypes and the corresponding phenotypes leading to their functions. Thus, it would be desirable to decipher all possible splice variants of a gene along with their expression/tissue specificity.